Variação Climática Secular e Mapeamento do ‘Efeito Estufa’ no Território Brasileiro

Abstract

Borehole temperature data from the eastern parts of Brazil has been examined in an attempt to extract information on surface thermal perturbations of the recent past at low latitudes. Forward models were employed in the analysis of temperature logs from 29 localities and, in addition, inverse modeling was carried out for data from 10 selected sites. The model results have allowed determination of the magnitude as well as the duration of ground surface temperature (GST) changes in five major geographic zones of Brazil. Prominent among such events are the warming episodes that occurred over much of the subtropical highland regions in the southeastern parts of Brazil. The present magnitude of GST changes in this region are in the range of 2 to 3.5 o C but have had their beginning during the early decades of the 20 th century. Nearly similar trends are also seen in temperature-depth profiles of bore holes in the subtropical humid zones of the interior parts of southern Brazil. In the coastal areas however, the magnitudes of surface warming are relatively smaller (falling in the range of 1.7 to 2.2 o C) while its beginning appears to have shifted to the mid decades of the 20 th century. The data from semi arid zones of northeast Brazil also indicate occurrence of surface warming events but the magnitudes are in the range of 1.4 to 2.2 o C while the duration of the warming event is larger, extending back into the last decades of the 19 th century. The present work also includes preliminary inferences on GST variations in the northern tropical regions of Brazil, based on analysis of borehole data in shallow wells at two localities: Belem (state of Para) and Manaus (state of Amazon). Surface temperature changes inferred for these localities are relatively small, being less than 1 o C in areas where the vegetation cover has been removed. In areas of tropical rain forest GST changes are found to be less than 0.5 o C. There are indications that changes in both climate and vegetation cover contribute to variations in GST. Another important result emerging from model studies is that the climate was relatively cooler during the 17 th and 18 th